轉載自:http://blog.itpub.net/22884147/viewspace-1103854/
package synthetic;
public class SyntheticMethodTest1 {
private A aObj = new A();
public class A {
private int i;
}
private class B {
private int i = aObj.i;
}
public static void main(String[] args) {
SyntheticMethodTest1 me = new SyntheticMethodTest1();
me.aObj.i = 1;
B bObj = me.new B();
System.out.println(bObj.i);
}
}
JVM是如何處理這個的?JVM是不知道類是內部的還是說嵌套的。JVM對所有的類對一視同仁,都認爲是頂層的。所有的類都會被編譯的頂層的類,那些內部類編譯完後會生成...$... class的類文件。
$ ls -Fart
../ SyntheticMethodTest2$A.class MyClass.java SyntheticMethodTest4.java SyntheticMethodTest2.java
SyntheticMethodTest2.class SyntheticMethodTest3.java ./ MyClassSon.java SyntheticMethodTest1.java
package synthetic;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
public class SyntheticMethodTest2 {
public static class A {
private A(){}
private int x;
private void x(){};
}
public static void main(String[] args) {
A a = new A();
a.x = 2;
a.x();
System.out.println(a.x);
for (Method m : A.class.getDeclaredMethods()) {
System.out.println(String.format(\
生成的這些方法的名字都取決於具體的實現,最後叫什麼也不好說。我只能說在我運行的這個平臺上,上述程序的輸出是這樣的:2
00001008 access$1
00001008 access$2
00001008 access$3
00000002 x
--------------------------
00000111 void wait
00000011 void wait
00000011 void wait
00000001 boolean equals
00000001 String toString
00000101 int hashCode
00000111 Class getClass
00000111 void notify
00000111 void notifyAll
--------------------------
00000002 synthetic.SyntheticMethodTest2$A
00001000 synthetic.SyntheticMethodTest2$A
00001008 SYNTHETIC|STATIC
00000002 PRIVATE
00000111 NATIVE|FINAL|PUBLIC
00000011 FINAL|PUBLIC
00000001 PUBLIC
00001000 SYNTHETIC
package synthetic;
import java.lang.reflect.Method;
import java.util.LinkedList;
public class SyntheticMethodTest3 {
public static class MyLink extends LinkedList<String> {
@Override
public String get(int i) {
return \"\";
}
}
public static void main(String[] args) {
for (Method m : MyLink.class.getDeclaredMethods()) {
System.out.println(String.format(\"%08X\", m.getModifiers()) + \" \" + m.getReturnType().getSimpleName() + \" \" + m.getName());
}
}
}
List<?> a = new MyLink();
Object z = a.get(0);
它不能調用返回String的方法,因爲List裏沒這樣的方法。爲了解釋的更清楚一點,我們重寫下add方法而不是get方法:
package synthetic;
import java.util.LinkedList;
import java.util.List;
public class SyntheticMethodTest4 {
public static class MyLink extends LinkedList<String> {
@Override
public boolean add(String s) {
return true;
}
}
public static void main(String[] args) {
List a = new MyLink();
a.add(\"\");
a.add(13);
}
}
我們會發現 這個bridge方法public boolean add(java.lang.Object);
Code:
Stack=2, Locals=2, Args_size=2
0: aload_0
1: aload_1
2: checkcast #2; //class java/lang/String
5: invokevirtual #3; //Method add:(Ljava/lang/String;)Z
8: ireturn
不僅調用 了原始的方法,它還進行了類型檢查。這個是在運行時進行檢查的,並不是JVM自己來檢查。正如你所想,在18行的地方會拋出一個異常:
Exception in thread \"main\" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String
at synthetic.SyntheticMethodTest4$MyLink.add(SyntheticMethodTest4.java:1)
at synthetic.SyntheticMethodTest4.main(SyntheticMethodTest4.java:18)